Choshek

Legendary Resistance (3/day). If the Choshek would fail a saving throw, it can choose to succeed instead.

Magic Weapons. The Choshek's weapon attacks are magical.

Dark Reflection. The Choshek’s passive perception is 20, and it knows the distance and direction of all mirrors or fully reflective surfaces within a five mile radius of it, and can see the area surrounding these surfaces as if using Clairvoyance. To all who can see them, these reflective surfaces become dark and cloudy, as if obscured by black smoke.

Inkwell. The Choshek can occupy another creature's space and vice versa, and the Choshek can move through any opening large enough for a small creature. The area within the Choshek’s space is obscured in foul magical darkness. A creature with darkvision can’t see through this darkness. Nonmagical light, as well as light created by spells of 8th level or lower, can't illuminate this area. Whenever a hostile creature starts its turn within this darkness, it must make a DC 18 Wisdom saving throw, taking 18 (4d8) psychic damage on a failed save, or half as much damage on a successful one.

Innate Spellcasting. The Choshek's spell casting ability is Charisma (spell save DC 18, +10 to hit with spell attacks). It can innately cast the following spells, requiring no material components:
At will: Mind Spike (4th level/5d8), Darkness, Major Image.
3/day each: Eyebite, Confusion, Enervation, Synaptic Static, Dimension Door
1/day each: Weird, Control Weather, Maddening Darkness.

Spell Refraction. The Choshek has advantage on saving throws against spells and magical effects. Additionally, whenever the Choshek is targeted by a line spell, a spell which requires an attack roll, or a spell which targets only the Choshek, roll a d6 and consult the following table:

d6    Roll Effect

1-2     The spell is absorbed, and has no effect.

3-5   The spell is scattered. Calculate the spell damage or duration and divide it evenly among all creatures within 60 ft of the Choshek, treating the Choshek as the caster. If a save is required to reduce the damage or mitigate the effect, affected creatures must make the save using the original caster's save DC. On a success, they take half the divided damage and avoid any other effects.

6      The spell targets the original caster as if cast by the Choshek. If required to make a saving throw, the caster must make the save using his own save DC.

Spells that deal radiant damage ignore this ability.

Siphoning Subjugation. If a creature is killed by the Choshek, the Choshek learns everything there is to know about the dead creature, and the creature rises in 1d4 rounds as a Nothic under the Choshek’s control.

Multiattack. The Choshek may use its Void Sight or cast an at-will spell. It then makes two Slam attacks.

Slam. Melee Weapon Attack: +14 to hit, reach 10 ft., 1 target. Hit: 21 (3d8 + 8) bludgeoning damage plus 13 (3d8) necrotic damage.

Void Sight. The Choshek attempts to peer into the deep recesses of a target's mind. One creature that the Choshek can see (including with its Dark Reflection ability) must make a DC 18 Wisdom saving throw or take 22 (4d10) psychic damage and become stunned for one minute as the Choshek learns one of the creature's greatest secrets, regrets, or hidden taboos. On a successful save, the target only takes half damage and doesn't become stunned, and the Choshek learns nothing about the creature. If the target succeeds on the saving throw by 5 or more, it becomes immune to Void Sight for 24 hours. A stunned creature may repeat the save at the start of each of its turns, ending the effect on a success. 

The Choshek can take 3 Legendary Actions, choosing from the options below. Only one legendary action can be used at a time, and only at the end of another creature's turn. Spent legendary Actions are regained at the start of the Choshek’s turn.

Move. The Choshek moves up to half its speed.

Slam (Costs 2 Actions). The Choshek makes one slam attack.

Void Sight (Costs 2 Actions). The Choshek uses its Void Sight ability.

Tides of the Void (Costs 3 Actions). The Choshek summons 2d4 Nothic, which appear in an unoccupied space within 30 feet of the Choshek and act as its allies and servants. Alternatively, the Choshek summons 1d4 Nothic in an unoccupied space within 20 feet of a reflective surface affected by its Dark Reflection ability. The Choshek can have no more than 12 nothics summoned with this ability at a time. Summoned Nothics remain until they or the Choshek dies, or until the Choshek dismisses them as an action.